A birth doula is a specially-trained person, usually female, who provides emotional and physical support to a pregnant and birthing woman (and her partner). In my case, I trained at the Center for the Childbearing Year in Ann Arbor, Michigan, in August 2009, which consisted of a course on childbirth education and a course on providing said support. A doula may choose to become certified through an organization such as DONA International, which indicates that she has also done a certain amount of required reading on birth and breastfeeding and attended a certain number of births as the primary doula. This is the path that I am currently on; I expect to be certified after the New Year!
That is, in a nutshell, what a birth doula does. So, what doesn’t a birth doula do? A birth doula is not trained in managing pregnancy or birth like a nurse, midwife, or OB is. She cannot give you medical advice or provide prenatal health care. She also cannot speak on your behalf during your labor. But she does know about common medical procedures and can help you seek or avoid them as you desire; she also knows about alternative (non-medical) methods for pain management and ways to help labor progress naturally, such as position changes. And she also stays with you during your entire labor, allowing your partner the freedom to come and go as needed and assist in the way that feels most comfortable to him or her, and giving both of you peace of mind in a sometimes stressful setting. Especially during hospital births, it can be reassuring to have a familiar face in the room that is attached to a person who understands what is going on!